The G2.1 series only has 1 tamper size for the 1.5L Jug: 19.5 CM
Insert the tamper into the Jug all the way while the blender is off. The tamper should hover above the blades.
If the tamper is touching the blades check if:
- You are using the correct tamper supplied with the blender
- The blender is assembled correctly.
- The tamper or jug are not damaged